The purpose of this research project is to develop a high-performance tunable optical filters suitable for wavelength division multiplexing by using high-precision LiNbO_3 piezoelectric actuators. The results obtained in this project are as follows :(1) A Fabry-Perot tunable optical filter built in a pair of optical-fiber connector ferrules has been designed and fabricated. Dielectric mirrors of high reflectivity are formed on a polished end of fibers to form a Fabry-Perot etalon, and the cavity length is varied by two piezoelectric actuators made of 140ﾟ rotated Y-cut LiNbO_3 single crystals. A tunable optical filter having a free spectral range of 14nm, a finesse of 140, and a FWHM of 0.1nm has been obtained. However, a small amount of hysteresis is observed that might be caused by friction between the ferrules and a metallic sleeve.(2) Another type of Fabry-Perot tunable filter that employs a pair of quartz plates with dielectric mirrors as an etalon is presented. The mirrors are placed in a path of a collimated optical beam, and the etalon spacing is controlled by a bending or a stretching actuator made of 140ﾟ rotated Y-cut LiNbO_3 single crystals. These filters work well, but further investigation is required to improve the filter performance.光ファイバ・ファブリーペロ-共振器として、反射率98%の誘電体多層反射膜を形成した石英製エタロン板2枚を向かい合わせ、両者の間隙を共振器とする構造のフィルタを構成した。レンズ付き光ファイバを用いてコリメートされた空間光を作り、LiNbO_3140°回転Y板伸縮変位アクチュエータあるいは板厚の半分まで自発分極を反転させた同種の結晶板による圧電単体屈曲変位アクチュエータに装着したエタロン板をその光路に挿入し、実験を行った。熱膨張係数の小さい材料で共振器部分を指示した結果、いずれの構成においてもアクチュエータへの印加電圧に対して比較的再現性の良いフィルタ特性が得られることが明らかになった。